This reminds me of a funny story a Danish friend told me. According to him Denmark has no natural rock - none, zilich. If you are a rockclimber you either go to the gym or drive to nearby Sweden. Anyway - about 10 years ago they built a massive bridge between Denmark and Sweden (it was a ferry previously). In the process of building the bridge they did a lot of dregding and construction - and they un-earthed some large boulders from under water and dumped them on the Danish coastline. Apparently they didn't last more than a few hours before local climbers jumped the construction fence, scrubbed the barnacles off and had them chalked and climbed. The first rock-climbs in Denmark! I have no idea how true this story was but he showed me some funny photos at the time...

On 24/06/2013 Snappy wrote:>Granite is among the more dense rock, so you would expect sandstone/trachyte>boulders to be a little lighter. Although then you would have to bubble>wrap them as they are more fragile... :)

Really?
Why is it that so many climbers think they are geologists?
Really, I'd prefer a bland wiki reference than an uninformed opinion.

I am no geo but I know that trachyte is of volcanic origin and like granite, dolerite, basalt and probably a lot of other rock types can be way up there in the density and non brittle stakes.
Sandstone by comparison is sedimentary and that is another story.

You can do the wiki thing if it has anything relevant to prove me wrong.

On 24/06/2013 Duang Daunk wrote:>On 24/06/2013 Snappy wrote:>>Granite is among the more dense rock, so you would expect sandstone/trachyte>>boulders to be a little lighter. Although then you would have to bubble>>wrap them as they are more fragile... :)>>Really?>Why is it that so many climbers think they are geologists?>Really, I'd prefer a bland wiki reference than an uninformed opinion.>>I am no geo but I know that trachyte is of volcanic origin and like granite,>dolerite, basalt and probably a lot of other rock types can be way up there>in the density and non brittle stakes.>Sandstone by comparison is sedimentary and that is another story.>>You can do the wiki thing if it has anything relevant to prove me wrong.>>
Unfortunately the wiki articles for other kinds of rock aren't as well layed out as the granite one. However I found this: http://geology.about.com/cs/rock_types/a/aarockspecgrav.htm
Granite: 2.6-2.7g/cm^3
Rhyolite: 2.4-2.6g/cm^3 (so a little lighter, but not as much as I would have thought).
Sandstone: 2.2-2.8g/cm^3

That doesn't give a complete picture, as the porosity of the different kinds of rock comes into play. My assumption (which you can feel free to disregard, or google, if you want) is that extrusive rock such as rhyolite would have a higher porosity than intrusive rock such as granite.

Another way of looking at it that has nothing to do with geology: I have picked up small granite, rhyolite and sandstone blocks and found I could lift different sizes of each, ergo, different mass per volume